Telephony users have long had to deal with a proliferation of user devices (sometimes referred to as ‘user equipment’ or ‘endpoints’) through which third parties may contact them. For example, a user might have a fixed-line (or ‘wireline’) telephony user device for use at home, a further fixed-line telephony user device for use in the office, and a mobile telephony user device for use whilst on the move. Each type of telephony device has associated advantages; whilst a mobile telephony device provides the user with mobility, a fixed-line telephony device can provide more reliable communications with no battery recharge concerns.
Users may also have a number of different access technologies available through which their telephony user devices may conduct communications. For example, a telephony user device may be equipped with a circuit-switched communication interface and one or more circuit-switched communication clients for conducting communications via suitable circuit-switched networks. Likewise, a telephony user device may also/alternatively be equipped with a packet-switched communication interface and one or more packet-switched communication clients for communicating via suitable packet-switched networks.
A circuit-switched telephony device may comprise a fixed-line Plain Old Telephone Service (POTS) telephone equipped with a circuit-switched interface and communication client for conducting communications via a Public Switched Telephone Network (PSTN). A circuit-switched telephony user device may comprise a mobile (or ‘cellular’) telephone equipped with a wireless circuit-switched interface and communication client for conducting communications via a cellular network such as a Global System for Mobile Communications (GSM) network or Code Division Multiple Access (CDMA) network.
More recently, packet-switched telephony devices have proliferated which may take the form of a fixed-line Internet Protocol (IP) telephone equipped with a fixed-line packet-switched interface and communication client for communicating via an Internet Protocol (IP) network, such as the internet or an IP Private Branch Exchange (IP-PBX). Similarly, a user may conduct communications via a personal computer (PC) equipped with a packet-switched communication client for conducting communications over the internet via a fixed-line internet connection. A mobile packet-switched telephony device may take the form of a portable computing device, such as a laptop or tablet, equipped with a wireless packet-switched interface and communication client for communicating via an IP network, such as the internet, using a WiFi™ or Bluetooth™ compliant wireless access point. A packet-switched communication client may conduct communications according to an internet telephony protocol, commonly referred to as Voice over Internet Protocol (VoIP), with associated setup and/or control protocols such as the Session Initiation Protocol (SIP) or H.323.
Increasingly, telephony user devices are available that are equipped with multiple communication interfaces to facilitate communication via multiple access technologies. For example, a modern “smartphone” is typically equipped with a circuit-switched interface for communicating via a cellular network and a packet-switched interface for communicating via the internet. Commonly, a smartphone may be equipped with several packet-switched interfaces, for example, a short-range radio interface, e.g. WiFi or Bluetooth™ compliant, and/or or via an interface for communication of packet data through a cellular network, such as 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), LTE-Advanced (LTE-A), High Speed Packet Access (HSPA), Wideband Code Division Multiple Access (W-CDMA) or Mobile WiMax etc. In such cases, a packet-switched communication client may also be deployed for conducting communications via one or more of the available wireless packet-switched interfaces. In cases such as this where a device is equipped with more than one communication client, the various clients deployed in that device are referred to as co-located. A suitable packet-switched communication client may be deployed on a user equipment prior to sale, or could be deployed subsequently through an application distribution portal such as the Apple® App StoreSM or Android™ Market etc.
To avoid confusing calling parties with identifiers such as telephone dialling numbers for each of the various communication clients of a user, a one-telephone dialling number telephony service allows the user to publish a single telephone dialling number on which they can be contacted. Using a simultaneous ringing service, when the single telephone dialling number is called, more than one of the user's communication clients will ring simultaneously. The user is then able to answer the call using the communication client of his choosing.
However, conventional systems provide a poor user experience in circumstances where the user's communication client experiences a loss of connectivity during an established communication session. It would therefore be desirable to provide improved methods, systems and apparatus for conducting communications in such a telecommunications system.